Just checked it and unfortunately it keeps taking ~30 seconds to start playing the music. To be clear with my steps: I exported with the latest GDevelop version and replaced soundmanager.js with yours, keeping the Howler line in the index and also keeping the soundtools.js from the latest version.
As a side note, today I installed Node.js and noticed the Export to iOS or Android option in GDevelop now always minify the code (with no way to disable it), so I had to uninstall Node.js in order to replace soundmanager.js
I think it may be useful to being able to uncheck the minify option when exporting to Android, just like when you export to a website.
Thanks again for your time.